Cross machine control in papermaking



Oct. 22, 1968 P. F. SPRINGUEL 3,407,114

CROSS MACHINE CONTROL IN PAPERMAKING Filed Jan. 4, 1965 2 Sheets-Sheet 1 IN VE N TOR Paul E SPRINGUEL PATENT AGENT 1968 P. F. SPRINGUEL 3,407,114

CROSS MACHINE CONTROL IN PAPERMAKING Filed Jan. 4, 1965 Q Q w i 2 Sheets-Sheet 2 l5 ,1; 4'2 lb 5 5 3 '5 2: a 2/ CROSS MACH/NE SAMPLING STAT/0N5 PATENT AGENT United States Patent 3,407,114 CROSS MACHINE CONTROL IN PAPERMAKING Paul F. Springuel, 37 Route de Genval, Ohain, Belgium Filed Jan. 4, 1965, Ser. No. 423,032 3 Claims. (Cl. 162-341) ABSTRACT OF THE DISCLOSURE The present invention relates to means associated with the usual head box of a papermaking machine, which enables to add a liquid to the stock in the headstock at spaced points across the headbox and in an adjusted manner, so as to considerably improve the cross machine weight uniformity of the paper. Addition of the liquid changes the consistency of the stock crosswise of the machine.

This invention relates to an apparatus and method of more easily obtaining and of improving the cross machine uniformity of paper sheets.

With the advent of new and faster techniques in paper converting, improvements in paper uniformity are being necessitated. For this and other reasons, more and more attention has been given to paper uniformity over the past few years; however, prior to the present invention, no simple means for improving the cross machine weight uniformity was available.

Current practice of obtaining cross machine weight uniformity uses a complex system of adjustment of the slice opening on the flow box. Adjustments are made 10- cally across the flow box by raising or lowering the top slice lip. Generally, a very high relationship exists between the weight and slice opening profiles, which indicates that one of the main causes of poor weight profile is poor adjustment of the top slice lip.

The present invention uses a substantially uniform slice opening for any given basis weight paper being produced. Control of the cross machine weight is made by locally changing the consistency by local addition of liquid at appropriate spaced points. In other words, applicant's invention relates to a method and apparatus for controlling the cross machine paper uniformity 'by consistency adjustments across the flow box.

Thus, it is an object of the invention to provide a simple but effective system of controlling the cross machine weight profile.

A further object of the invention is to provide a flow box wherein a locally adjustable slice lip may be dispensed with.

Further features, objects'and advantages will be evident from the following details description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a paper machine headbox incorporating the present invention;

FIGURE 2 schematically illustrates the apparatus shown in FIGURE 1 in cross-section; and

FIGURE 3 shows plots of basis weight and caliper of paper produced comparing the invention with known methods.

In FIGURE 1 there is shown a conventional headbox 1 mounted in a suitable manner at the head or wet end of the paper machine which includes the breast roll R, on which is trained the travelling wire screen W. The headbox 1 includes the usual stock inlet 2 and a front wall 3 spaced from the apron plate 4 to form a stock or slice outlet 5. The front wall may be moved to vary the opening 5 to obtain the conditions required for a given fabrication. A conventional holey roll 6 is mounted in the box adjacent the slice opening.

In a conventional machine the slice opening 5 is ad- 3,407,114 Patented. Oct. 22, 1968 justable locally, usually by adjustment of a flexible slice lip. Such local adjustments are usually made by tightening or loosening tie bolts or the like to thereby locally vary the size of the opening.

Since these local adjustment means are unnecessary with applicants system, the top slice may simply be a straight edge to provide a substantially uniform slice opening transversely of the machine. Suitable means (not shown) such as means regularly supplied on flow boxes for moving the slice as a unit to change flow conditions, may similarly be used when changing flow conditions with applicants system. Thus, the slice lip may be moved as a unit to change the slice opening for different basis weight papers; however, care must be taken to ensure the slice opening uniformity.

Similarly, if the present invention is applied to existing flow boxes with local adjustment means, the slice opening must be adjusted to be as uniform as possible before startup, for optimum results.

As illustrated, there is provided a plurality of individual open ended pipes 7 extending into the headbox 1 from a suitable header 8. These pipes open into the headbox. The holey roll 6 is located downstream from the pipe outlets. Connections including a pressure regulartor 9 are made for supplying a suitable liquid, such as fresh water to the header 8. Each pipe 7 is provided with a suitable valve 10 to control the flow of water into the headbox. The slice opening is held substantially uniform across the machine, but may be increased adjacent the edges, if desired. The Wider outlet adjacent the edge of the headbox is usually used to accommodate the pressure drop caused by the side wall of the flow box or other disturbances.

In one particular setup the holey roll 6 has a plurality of transverse baffles and the pipes 7 are spaced apart distances equal to the baffle spacing or some multiple thereof. It may be generally stated that the more pipes 7, the greater the accuracy of control that may be achieved; however, if too many pipes are used the flow of stock may be obstructed. Furthermore, lateral flow of added water requires a certain minimum spacing of pipes for the system to be effective. This minimum spacing, of course, depends partially on the maximum flow through each pipe. These pipes will usually be spaced about 2 to 15 inches apart, preferably 4 to 10 inches. While the pipes 7 are shown above the level L (see FIG. 2) of stock in the headbox, it is also permissible to have the ends of pipes 7 submerged.

The location of the outlets of pipe 7 with respect to the holey roll 6 and slice opening 5 is not too critical. These outlets must, however, be located upstream from the holey roll to allow dispersion of the added water in the stock by the action of the holey roll and thus prevent streak formation on the sheet. Similarly, these outlets from pipes 7 must be located sufficiently near the holey roll 6 so that the individual water additions through pipes 7 will not spread too far laterally across the machine. The location for the outlet of pipes 7 will best be determined for a given installation by trial. In one par ticular application, these distances were about 2 /2 feet above the floor of the box and about 1 foot in from the front wall with the outlets being approximately tangent to the rearmost point on the holey roll 6.

When operating the present invention in accordance with the water line on the wire as in conventional paper machine control, results comparable with slice opening adjustments are easily obtained. The various valves 10 are adjusted to vary the flow through pipes 7 until a straight water line perpendicular to the machine direction is obtained. With the present system, it is easy to make the required adjustment as the valve 10, requiring adjustment, is usually directly behind the discrepancy in the water line on the wire. Removal of a discrepancy with conventional slice opening adjustment is relatively complex, as the discrepancy and point on the slice that must be adjusted usually are not in line.

Applicants system can also be operated by feeding stock to the headbox at a consistency higher than that required and opening all the valves the same amount to add sufiicient water to adjust the consistency to that required. Under these conditions, local adjustment to obtain a uniform basis weight across the machine may be made by increasing or decreasing the amount of water supplied at spaced points as required (i.e., by opening or closing valves 10).

Adjustments of the valves 10 may be based on information other than the water line on the wire, which information provides an accurate picture of the cross machine weight profile. This information may be obtained by actual sample measurements across the reel at the dry end of the machine. To obtain accuracy, it is sometimes advisable to measure a plurality of samples along a transverse line in the paper. The maximum number of sample measurements taken across the machine should be equal to the number of down pipes 7.

One method of control of the valves 10 from the sample measurements include plotting a curve of basis weight versus cross machine width and positioning a transparent guide indicating the location of the pipes 7 across the machine over the curve. It is then evident which valves 10 must be manipulated and with experience how much each valve must be opened or closed to produce a relatively uniform basis weight sheet. With applicants system the valves requiring adjustment are usually directly in line with the points where the basis weight must be corrected. Thus, with applicants system the basis weight across the machine is measured and the amount of water locally added is adjusted in accordance with the measured basis weight.

It is helpful for reproduction of results to have a flow meter on each down pipe 7 so that the flow through each pipe may be measured.

The following is a specific example of a specific arrangement on one machine. 13 pipes 7 were evenly spaced at 10% in. intervals across an open headbox of a paper machine. The pipe size used was 1 in. ID. and the pipes were located on a tangent to the rearmost point on the holey roll 6. The ends of the pipes were above the level of liquid in the headbox, being 31 inches above the floor of the flow box.

The results obtainable using the above arrangement compared with conventional operation on the same machine are illustrated in FIG. 3. The curves marked a and d indicate basis weight (weight in pounds per 3,000 square feet of paper) and caliper (sheet thickness in mills) for a typical run before application of applicants invention; curves b and e indicate basis weight and caliper for a uniform slice opening without water addition through the pipes 7; and curves 0 and 1 illustrate results for basis weight and caliper obtained using applicants invention. Curves c and fwere obtained by testing a sheet made with valves 4, 5, 6, and 7, open two turns (these valves 4, 5, 6, and 7 control the flow of water at peak points corresponding to the large deviation shown in curve b). The pressure in header 8 was approximately 8 p.s.i.

For each of the above curves, 40-pound kraft paper was being produced andthe average slice opening was 1% inches. The basis weight and caliper were determined on 76 square inch samples (cross direction 9 /2 inches x machine direction 8 inches).

It is believed that the point of large deviation on curve b for a uniform slice opening was caused by defects in the stock approach system. This defect was not appreciated before applicants system was applied.

From the above, it is evident that curves a and d of FIG. 3 show large discrepancies in the formed sheets.

4 Applicant has been able to reduce these discrepancies in the above example, as indicated by curves c and f.

To more particularly show the comparison between the prior art and applicants invention, calculations of the average deviations A and A were made. Average deviations A and A are defined as follows:

2 standard deviation of basis weight dataX Average of basis weight data 2 standard deviation of caliper dataX 100 Average of caliper data percent caliperX 1000 basis weight;

curves a and d gave A" 5.5%; curves b and e gave A=7.3%; and curves c and gave A"=2.9%.

Mullen tests, expressed as a percentage of the basis weight, were also conducted and the average deviation A calculated. The following results were obtained:

A': 13.4% for run under usual conditions;

A"'=9.1% for run with uniform slice opening without water addition through pipes 7; and

A'=7.9% for run in accordance with applicants invention.

Other tests were also conducted and they also showed a marked increase in the cross machine uniformity of the paper sheets. For instance, moisture content measurements showed a marked increase in uniformity across the paper sheets.

For the values of A, A, A", and A, 9 /2 inches at each edge of the web of paper were disregarded. The slice opening was not enlarged at the ends. By increasing the number of pipes 7 and thus reducing the spacing between these pipes, even more accurate control is possible.

It is important to have the slice opening as close to uniform as possible; in the above specific example, the deviation for a 1% inch opening was '.008 inch. Higher deviations are permissible, but it is better to reduce these deviations as much as is practical.

It is noted that, if the total fiow through the flow box is changed, a change will be required in the openings of valves 10.

Fresh water should be used in header 8 if optimum results are to be obtained, in particular with filled paper. White water tended to result in streak formation in filled sheets.

The pressure in header 8 should not be too high or the jet from the pipes 7 may cause formation difiiculties. This pressure should preferably be less than about 15 to 20 p.s.i., preferably in the range of about 6 to 12 p.s.i. for open flow boxes, and should be kept substantially constant.

While the disclosure has shown only a single row of pipes 7, it is evident that more than one row may be used and that the pipes in these rows may be staggered. Simi larly, the disclosure has referred only to Fourdrinier machines, but the invention may also, with minor adjustments, be applied to cylinder machines.

If an appropriate instrument mounted on the paper machine is available to obtain the cross machine basis weight profile and if the values 10 are automatic, it would be possible to control them in dependence with the output of this instrument and so obtain automatically a uniform cross machine basis weight sheet.

Thus, applicant has disclosed a simple but effective system of controlling the cross machine weight profile on a paper machine, with resulting improvements in the cross machine profile of other properties, such as thickness and moisture content. While this application has described only a Fourdrinier machine, the principle of the invention may readily be applied to a cylinder machine.

It is understood that the term paper is used in the generic meaning and includes sheet materials made from all kinds of fibrous materials in liquid suspension, such as cartons, fibreboards, felts, and the like.

What I claim is:

1. In a papermaking machine, a flow box comprising 10 extending across said box adjacent said slice outlet and 15 spaced downstream from the outlets of said pipes so that the liquid discharged from said pipes will be dispersed 6 t in said stock by the action of said holey roll, the minimum spacing between said pipes being such as not to obstruct the flow of stock and allow lateral flow of added liquid and also depending on the maximum fluid flow through each pipe.

2. A flow box as claimed in claim 1, wherein the liquid fed to said pipes is fresh water.

3. A flow box as claimed in claim 1, wherein the pipe outlets are downwardly directed towards the bottom of said flow box.

References Cited UNITED STATES PATENTS 1,662,226 3/1928 Witham 162344 DONALL H. SYLVESTER, Primary Examiner.

A. C. HODGSON, Assistant Examiner. 

